Eloquent polymorphic relationships explained (with examples)

In my opinion, Eloquent is one of the most powerful features of Laravel. It is an API for interacting with your database, and it has a very nice and easy-to-remember syntax. For example:

$post->author->name;

Will give you the name of the post’s author.

This is an example of an Eloquent relationship. Relationships define how your models (tables) are connected. Although most are easy to understand, there are a few more complicated ones.

In this post, I’m going to show how every relationship works.

One to one

In this example, we have three models: a Post, a Video, and an Image.

• A Post has one Image
• A Video has one Image
• An Image belongs to a Post or Video

And we have this table structure:

posts
    id - integer
    title - string
videos
    id - integer
    name - string
images
    id - integer
    path - string
    imageable_id - integer
    imageable_type - string

We can define these relationships like this:

// app/Models/Post.php
public function image()
{
    return $this->morphOne(Image::class, 'imageable');
}
// app/Models/Video.php
public function image()
{
    return $this->morphOne(Image::class, 'imageable');
}
// app/Models/Image.php
public function imageable()
{
    return $this->morphTo();
}

Now we can access the image like this:

$post->image->path;
$video->image->path;

And if we have the $image, we can get the object where it belongs to (a Post or a Video) like this:

$image->imageable;

One to many

In this example, we have three models: a Post, a Video, and a Comment.

• A Post has many Comments
• A Video has many Comments
• A Comment belongs to a Post or a Video

And we have this table structure:

posts
    id - integer
    title - string
videos
    id - integer
    name - string
comments
    id - integer
    body - string
    commentable_id - integer
    commentable_type - string

We can define the relationships like this:

// app/Models/Post.php
public function comments()
{
    return $this->morphMany(Comment::class, 'commentable');
}
// app/Models/Video.php
public function comments()
{
    return $this->morphMany(Comment::class, 'commentable');
}
// app/Models/Comment.php
public function commentable()
{
    return $this->morphTo();
}

Now we can access the comments like this:

foreach($post->comments as $comment) {
    //
}
foreach($video->comments as $comment) {
    //
}

And if we have a $comment, we can get the corresponding model (a Post or a Video) like this:

$comment->commentable;

Many to many

In this example, we have three models: a Post, a Video, and a Tag.

• A Post has many Tags
• A Video has many Tags
• A Tag belongs to many Posts or Videos

For example, a Tag called "personal" can belong to a ``Post**and** aVideo`.

We may have this table structure:

posts
    id - integer
    title - string
videos
    id - integer
    name - string
tags
    id - integer
    name - string
taggables
    tag_id - integer
    taggable_id - integer
    taggable_type - string

We can define the relationships like this:

// app/Models/Post.php
public function tags()
{
    return $this->morphToMany(Tag::class, 'taggable');
}
// app/Models/Video.php
public function tags()
{
    return $this->morphToMany(Tag::class, 'taggable');
}
// app/Models/Tag.php
public function posts()
{
    return $this->morphedByMany(Post::class, 'taggable');
}
public function videos()
{
    return $this->morphedByMany(Video::class, 'taggable');
}

Now we can access the tags like this:

foreach($post->tags as $tag) {
    //
}
foreach($video->tags as $tag) {
    //
}

And if we have a $tag, we can access the posts and videos like this:

foreach($tag->posts as $post) {
    //
}
foreach($tag->videos as $video) {
    //
}